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The role of GTP binding and hydrolysis at the atToc159 preprotein receptor during protein import into chloroplasts

¹ Department of Biochemistry and Molecular Biology and Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, MA 01003
² Laboratoire de Physiologie Végétale, Institut de Botanique, Université de Neuchâtel, 2009 Neuchâtel, Switzerland

Correspondence to Danny J. Schnell: dschnell{at}biochem.umass.edu

The majority of nucleus-encoded chloroplast proteins are targeted to the organelle by direct binding to two membrane-bound GTPase receptors, Toc34 and Toc159. The GTPase activities of the receptors are implicated in two key import activities, preprotein binding and driving membrane translocation, but their precise functions have not been defined. We use a combination of in vivo and in vitro approaches to study the role of the Toc159 receptor in the import reaction. We show that atToc159-A864R, a receptor with reduced GTPase activity, can fully complement a lethal insertion mutation in the ATTOC159 gene. Surprisingly, the atToc159-A864R receptor increases the rate of protein import relative to wild-type receptor in isolated chloroplasts by stabilizing the formation of a GTP-dependent preprotein binding intermediate. These data favor a model in which the atToc159 receptor acts as part of a GTP-regulated switch for preprotein recognition at the TOC translocon.

© 2008 Wang et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jcb.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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This article has been cited by other articles:

• Agne, B., Infanger, S., Wang, F., Hofstetter, V., Rahim, G., Martin, M., Lee, D. W., Hwang, I., Schnell, D., Kessler, F. (2009). A Toc159 Import Receptor Mutant, Defective in Hydrolysis of GTP, Supports Preprotein Import into Chloroplasts. J. Biol. Chem. 284: 8670-8679 [Abstract] [Full Text]  

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